Tension device for needlethread of a sewing machine

ABSTRACT

The tension device disclosed is of the type which combines a pair of releasable spring-pressed tensioning disks with a torsion spring. When the pressure between the disks is released at the end of an operation, means are also provided to inactivate the torsion spring to prevent the latter from pulling the thread from the needle eye when the thread is cut or when the next operation is started.

United States Patent 1 1 [111 3,738,298 Albrecht [4 June 12 1973 [S4] TENSION DEVICE FOR NEEDLETHREAD 3,206,138 9/1965 Lindsey 242/150 X 0 A SEWING MACHINE 2,701,694 2/1955 Hamlett 112/254 X [75] Inventor: Ernst Albrecht, Hochspeyer/Pfalz, FOREIGN PATENTS 0R APPLICATIONS Germany 723,852 8/1942 Germany 112/254 [73] Assignee; Plaff Industriemaschinen Gmbfl, 675,102 4/1939 Germany 242/150 Kaiserlautern/Pfalz, Germany [22] Filed: Oct. 28, 1971 Primary ExaminerGeorge H. Krizmanich pp No 193 279 AttorneyOrville N. Greene and Frank Lowell Durr Foreign Application Priority Data [57] ABSTRACT 1970 Germany G 40 6745 The tension device disclosed is of the type which combines a pair of releasable spring-pressed tensioning (Cll. disks with a torsion p g when the pressure between [58] Fie'ld I254 255' the disks is released at the end of an operation, means 242 are also provided to inactivate the torsion spring to prevent the latter from pulling the thread from the needle [56] References Cited eye when the thread is cut or when the next operation ta t d. UNITED STATES PATENTS ls S r e 2,726,053 12/1955 Pagni 242/ 3 Claims, 4 Drawing Figures TENSION DEVICE FOR NEEDLETHREAD OF A SEWING MACHINE The invention relates to an apparatus for tensioning the needlethread of a sewing machine.

Tension devices of this type operate to restrain or brake the needlethread being drawn from a supply roll by the thread control means also called thread takeup or thread governor; they are an important auxiliary for obtaining uniform stitch formation.

It is usually customary for the tension apparatus of a sewing thread to be regulated by a thread tension check spring (also called thread regulator) which operates so that with the downward movement of the thread takeup lever, neither the loose needlethread will be pierced by the descending needle; nor the possibility of the development of twist remains.

The apparatus for the tensioning of needlethread must so strongly restrain the thread, that the resistance, which results from the thread drawn from the supply roll is greater than the resistance tha the thread encounters in stitch formation with the passage around the spool capsule and through friction in the sewed material.

The apparatus for tensioning of needlethread is as a general rule formed as two journaled-together cooperating thread-tension disks, between which the thread is passed. The contact pressure of both thread tension disks is determined by a tension spring, which exerts a pressure on one or both of the tension disks and which is adjustable with the aid of a regulating nut.

With these known apparatuses for the tensioning of thread, it is also usual and for the uniform stitch formation indispensable, to include a torsion spring as a thread tension check spring also called a thread regulator which is arranged in a housing, and in this housing is also fastened the supporting journal (pin) for the tension disks.

In order to guarantee a rational method of operation, it is desired that after finishing a seam forming process, before the separation of the sewed work piece, for the needlethread of the latter to be brought up to a predetermined thread length, so that upon the beginning of the next seaming process, the thread will not be extracted from the needles eye. This production of a predetermined needlethread length is, however, complicated through the braking or restraining action of the pressured stationary disks of the mechanism, for tensioning the needlethread.

In order to eliminate these drawbacks, it is known to. attach to the mechanism for tensioning of the thread, a rod for the removal of compressive stress on the thread tension disk. This releasing rod will thereby, as a rule, be supported in a journal pin of the threadtension disks. It is axially displaced through a suitable connection to the material presser bar, carrying the usual presser-foot and operates through an intermediate plate to open a tension spring holding the threadtension disks together.

With the so far known apparatus, the possibility exists that the material presser-bar, after finishing the seam process, will be lifted and that thereby through the releasing rod, the device for tensioning the needs lethread will be nullified'so that then a fixed length of the needlethread can be brought out before the separae tion of the sewed workpiece from the needlethread is effected.

The known apparatus works sufficiently and technically satisfactorily, so far as it is used with sewing machines where the thread is pinched only between a single pair of disks and inasmuch as the finished sew work technically permits that the tension spring be loosened before cutting the needlethread.

With many sewing machines and above all, with automatic sewing machines which are equipped with an arrangement for cutting off the needlethread, the heretofore known devices do not work satisfactorily. With sewing machines of this type, the needlethread is cut off when the needle bar is outside the sewed material and has already traversed beyond its upper position. The thread take-up lever is then in the high position. In this cutting position, the needlethread, under the influence of the last stitch of a seam, retracting thread takeup lever, brings the thread tension check spring to its bias position; This is simultaneously the starting position, the continuously lowering of the thread take-up lever starts the operating movement, which to begin with, consists in a needlethread drawing or stretching movement. The thread, at the high position of the needle bar, remains in the stretched position and thread take-up spring will thus, immediately after the finished separation of the needlethread, execute its performance or standard movement, and thereby draw the thread out from the needles eye.

Also, among sewing machines, in which the needlethread is led over two clamped disk pairs with differentailly clamping pressure, the known devices are no more trustworthy. Those consisting of a device for tensioning from a main and an auxiliary tensioning device are, most of all, untrustworthy when it is necessary to form at the end of a seam or a stitching group, some additional stitches for the locking or fastening mechanism, which make necessary a reduced needlethread tension.

In accordance with the present invention, the solution to the problem of preventing needlethread from being withdrawn from the needles eye depends not on the tensioning of the thread as such, but rather on slackening the movement of the thread tension check spring, after the thread is separated from the work piece. Thus, the invention is based on a mechanism arranged to fix the position of the thread tension check spring of the main clamping disk pair simultaneously with the. removal of clamping pressure between the tension disks thereof.

According to the invention, this problem is solved by providing the shank of the release rod for the main tension disk pair with a screw-form guide surface, providing a lock plate with a guide surface adapted to cooperate with the screw form guide surface so as to rotate the release rod as it is moved axially with respect to the lock plate, and providing rotatable means adapted to inactivate the thread torsion-check spring associated with said disk pair when rotated by movement of the release rod.

Thereby the release rod, during axial displacement, also receives a rotaty movement, which is transferred by means of the synchronizing bracket to a sleeve. The latter takes along the end of the check spring controlling the thread into an auxiliary tension position. Thus, the check spring is made inoperative.

A particularly simple arrangement for the control surface of the release bar is given by the arrangement of a the lock plate encircled by the synchronizing 3 bracket at a bushing-like house of the tension device. The lock plate also prevents the release rod from falling out of the longitudinal bore of the supporting pin.

In order to keep the prior dimensions of the tension device, according to a further object of this invention, the bushing is cut free in the movementzone of the synchronizing bracket and the jacket is provided with stops protruding into the cut-free area of the bushing-, like housing.

The invention is described by means of ,the drawing of one embodiment in which:

FIG. 1 shows a perspective view on an enlarged scale of the new tension device.

FIG. 2 is a detail perspective view to a similar enlarged scale, of the rod, with the lock plate in dashed line, for the screw-shaped control surface of the release rod, as well as a part of a material presser bar with an activating piece for the release pin.

FIG. 3 is an exploded view of the individual parts of the tension device of FIG. 1.

FIG. 4 shows the course of the needlethread through the tension device shown in FIGS. 1 and 3 and an additional auxiliary tension device, the thread being greatly enlarged for the sake of clarity.

The tension device shows a carrier plate 1 to be attached to the machine housing, a bushing-like housing 2 (FIG. 3) being fastened in said plate 1, the bushinglike housing 2 having borings 3, 4 of different diameters for receiving a longitudinally bored pin 5 and a sleeve 6, a torsion spring 7, hereafter called thread take-up spring, being disposed therein, one end of which is angularly bent and is inserted into a boring 8 (FIG. 3) of the pin 5 and the other, hook-shaped end 9 thereof, engaging the needlethread (NF) (FIG. 4), protruding from a recess 10, the boundary surface of said recess 10 forming stops 11, 12, and the spring end 9 controlling the needlethread (NF) being movable between said stops. The pin 5, together with the thread take-up spring 7 disposed thereon and the sleeve 6 is inserted into the boring 3 resp. 4 of the bushing-like housing 2 and fastened by means of a screw 13, whereby the collar 14 of the pin 5 abuts the front of the sleeve 6. On

the free shaft portion of the pin 5, which is longitudi-.

nally slit and partially provided with screw threads 15, are two tension disks or plates 16, 17, which can be pressed together by the intermediary insertion of release disk 19 provided with a cross-bar 18 fitted into the slot of the pin shaft part by the pressure of spring 20 which is adjustable by a regulating nut 21. The spring pressure effective on the tension disks 16, 17 can be released by means of a release pin or rod 22 in the step-shaped longitudinal bore of the pin 5, the cylindrical shaft part 23 of said rod 22 co-acting with the crossbridge 18 of the release disk 19. The release rod 22 further has a shaft part 25 provided with a screw-shaped control surface 24. Co-cating with the control surface 24 is guide surface 26 (FIG. 2) of a lock or guide plate 27, which is fastened to the bushing-like housing 2 with two screws 28. A synchronizing bracket 29 fastened to the shaft 25 of the release rod 22 has a forward end 30 which engages a slot guide 31 in the sleeve 6, saidslot guide running parallel to the longitudinal axis of the release rod 22. The bushing-like housing 2 in the zone of the rotatably positioned sleeve 6, which carries the slot guide 31, is partially cut free in order to enable the syn-. chronizing bracket 29 to carry out a certain rotating motion. To limit the rotating motion, the sleeve ,-6 is provided on both sides of the slot guide 31 with frontal projections 32.

The activation of the release rod 22 takes place by way: of an inclined surface 33 (FIG. 2) of a lifting bar 35 fastened on the partially shown material presser bar 34. Co-acting with the inclined surface 33 is the ballshaped front end 36 of the release pin 22.

To guide the needlethread (NF) there are disposed at the carrying plate 1 a guide pin 37, FIG. 4, an auxiliary tension device 38 and a thread guide 39. The tension device 38 must be regarded as an auxiliary device. It consists of a pin 40 resembling the pin 5, fastened in the carrying plate 1, atension disk pair 41 (only one shown) corresponding to the tension disks 16, 17, a tension spring 20 as well as a nut 21 being disposed on said carrying pin 40.

The needlethread (NF) is guided from a thread supply (not shown) in succession under the pin 37, between the tension disks 41 of the tension device 38, between the tension disks 1 6, 17, over the hook-shaped end 9 of the thread take-up spring 7 and under the thread guide 39 to a thread take-up lever (not shown), and from there is guided through the eye of the needle (also not shown). It should be mentioned that the tension disks 41 are under a lesser spring tension than the tension disks l6, 17. For this reason, after lifting of the spring pressure effective on the tension disks 16, 17, for instance, at the beginning and end of a seam, the locking stitches may be sewn with a lesser thread tension (which is more advantageous for locking the seam), than the stitches of the remaining seam and, upon pulling out of a thread at the end of the seam, it is sufficiently long for the following stitch formation because only the lesser frictional resistance of the auxiliary tension device 38 need be overcome.

The tension device operates as follows:

While sewing, the required length of needlethread (NF) for each stitch is pulled out from a thread supply by means of the take-up lever, whereby the tension disks 41 and l6, l7 produce a specific braking or restraining effect on the thread NF which is adjustable by means of the nuts 21. Thereby, through the pull on the thread NF, the hook-shaped end 9 of the thread takeup spring 7 is moved from its rest position I, in which the radial leg of the end 9 of the take-up spring 7 abuts the stop surface 12 of the sleeve 6, to its initial tension position shown in dotted lines in FIG. 4, in which position the above designated leg of the spring 7 under the pull occurring at the thread NF through the take-up lever abuts the stop surface 11. From this position, which is reached at the latest when the take-up lever guiding the thread (NF) is in its highest position, the thread is kept slightly tensed during the following thread-feeding phase by the thread take-up spring 7, in order to avoid its rushing ahead of the needle, forming loops in the path of the needle, and when the needle makes a stitch in this loop, causing tearing of the thread. The end 9 of the take-up spring 7 moves during the thread-feeding phase from its initial tension position" into the rest position I. Since the high position of the take-up lever is also the position in which the machine is at the end of a seam after the thread is cut or being stopped in order to cut the thread, and the braking effect of the tension device 38 on the thread NF surpasses the tension produced by the initial tension position II of the spring 7, the end 9 of the spring 7 engaging the thread NF would pull the end of the thread out of the eye of the needle when the thread is cut. In order to prevent this, in accordance with the present improvement, simultaneously with the lifting of the spring pressure effective on the tension disks 16, 17 the end 9 engaging the thread NF of the take-up spring 7 is brought from the rest position I into the initial tension position II, namely as follows: Upon lifting the material pressure shaft 34 with the lifting part 35, the release pin 22, by means of the inclined surface 33, the ball-shaped front end 36 of the release rod 22 cooperating therewith, is being axially displaced toward the tension disks 16, 17, whereby the forward end of the shaft part 23 of the release rod 22 strikes against the cross-bar 18 of the release disk 19 and through the latter compresses the tension spring 20 and lifts it off the tension disk 19, so that it can no longer have any effect on the tension disks 16, 17. During the axial displacement of the release rod 22 the latter, through the coaction of its screw-shaped control surface with the guide surface 26 of the lock plate 27, simultaneously receives a rotary movement, said rotary movement, through the synchronizing bracket 29 with its'frontal end 30 engaging in the slot guide 31 of the sleeve 6 is transferred to the sleeve 6. Through the stop surface 12 of the sleeve 6 the hook-shaped end 9 of the thread tension check spring 7 controlling the thread NF is carried along and brought from the rest position 1 into the preliminary tension position ll. This makes the tension check spring 7 inoperative. The end 9 of the spring 7 remains in the auxiliary tension position Il until the first stitches of the next following seam are formed. The tension spring 20 presses the release rod 22, after release through the inclined surface 33, back into the initial position by way of the cross-bar 18 of the release disk 19, whereby the tension spring 20 again presses the tension disks 16, 17 together and the hook-shaped end 9 of the spring 7 returns to the rest position I, so that the hook-shaped end 9 of the spring 7 can again perform its function.

The operation of the release rod 22 can, of course, take place by other means than the inclined surface 33 described in the present embodiment, in automatic sewing machines, for instance, by a cam of the usual control disk through a suitable lever connection independent of the lifting or lowering motion of the material-holding clamp.

I claim:

1. In a tension device for a needlethread of a sewing machine of the type having at least one pair of tension disks disposed on a bearing pin with a coil spring abutting at least one of the tension disks of the pair and being liftable from the tension disk by means of a release rod movably disposed in the bearing pin thereof which is axially bored to receive said release rod, said bored bearing pin being fastened in a bushing-like housing mounted on a carrier plate adapted to be fastened to the sewing machine housing, the improvement comprising,

a sleeve movably disposed in said bushing-like housing adapted to receive a torsion spring, said sleeve having a recess and a longitudinal slot parallel to the axis thereof,

said torsion spring being disposed in said sleeve and having a first end thereof fixed with respect to the bearing pin and a second, hook-shaped, needle thread controlling end protruding from the recess in said sleeve, said second end normally being in engagement with one end of the recess and being movable between the ends thereof,

said release rod having a screw-shaped control surface,

stationary guide means co-acting with the screwshaped control surface,

a synchronizing bracket on said release rod containing means to engage said longitudinal slot of said sleeve whereby axial movement of the release rod in releasing the spring on said tension disk also rotates the sleeve which in turn rotates said hookshaped end of the torsion spring via said one end of said recess which is in engagement with said hook-shaped end of the torsion spring to inactivate said thread controlling torsion spring.

2. The tension device as claimed in claim 1 comprising a lock plate fastened to said bushing-like housing and containing said stationary guide means, said lock plate being fastened in such a position that said synchronizing bracket encircles the same.

3. The tension device as claimed in claim 2 wherein said bushing-like housing contains an opening exposing the longitudinally slotted portion of the sleeve to the bracket, said sleeve containing projections which act as stops against the ends of the opening in the bushing-like housing. 

1. In a tension device for a needlethread of a sewing machine of the type having at least one pair of tension disks disposed on a bearing pin with a coil spring abutting at least one of the tension disks of the pair and being liftable from the tension disk by means of a release rod movably disposed in the bearing pin thereof which is axially bored to receive said release rod, said bored bearing pin being fastened in a bushing-like housing mounted on a carrier plate adapted to be fastened to the sewing machine housing, the improvement comprising, a sleeve movably disposed in said bushing-like housing adapted to receive a torsion spring, said sleeve having a recess and a longitudinal slot parallel to the axis thereof, said torsion spring being disposed in said sleeve and having a first end thereof fixed with respect to the bearing pin and a second, hook-shaped, needle thread controlling end protruding from the recess in said sleeve, said second end normally being in engagement with one end of the recess and being movable between the ends thereof, said release rod having a screw-shaped control surface, stationary guide means co-acting with the screw-shaped control surface, a synchronizing bracket on said release rod containing means to engage said longitudinal slot of said sleeve whereby axial movement of the release rod in releasing the spring on said tension disk also rotates the sleeve which in turn rotates said hook-shaped end of the torsion spring via said one end of said recess which is in engagement with said hook-shaped end of the torsion spring to inactivate said thread controlling torsion spring.
 2. The tension device as claimed in claim 1 comprising a lock plate fastened to said bushing-like housing and containing said stationary guide means, said lock plate being fastened in such a position that said synchronizing bracket encircles the same.
 3. The tension device as claimed in claim 2 wherein said bushing-like housing contains an opening exposing the longitudinally slotted portion of the sleeve to the bracket, said sleeve containing projections which act as stops against the ends of the opening in the bushing-like housing. 